Drill bit



F. H. DEILY DRILL BIT Sept. 5, 1961 2 Sheets-Sheet 1 Filed Dec. 11, 1957 ME IV "IIIII Fredric Hurry Deiiy Inventor By M di-Z1 Attorney United States Pflfifl 3 6.

2,998,857 DRILL BIT Fredric H. Deily, Tulsa, Okla, assignor, by mesne as; signments, to Jersey Production Research Company Filed Dec. 11, 1957, Ser. No. 702,039

" 9 Claims. (Cl. 175-359) The present invention pertains generally to the art of drilling boreholes, and it is concerned more particularly with an improved type of rotary, drill bit. The invention especially relates to a multi-cutter element rotary drill bit in which each cutter element is an assembly of cutters uniquely arranged to induce tensile stresses in a formation being drilled.

Multi-cutter element rotary drill bits have been widely adopted by the petroleum industry for use in drilling boreholes. Among the types of cutter elements that have been used in such bits are blades; toothed cones and rollers, and discs, Blades rely for their effectiveness primarily upon a scraping type of action, while rollers, discs and cones make use of various combinations of scraping, crushing and chipping actions.

Recently, it has been found that the process of drilling a borehole in the earth may be greatly improved by inducing tensile stresses within the rocks or other formations being penetrated. Rocks and other earthern structures have been observed to be much weaker in tension than they arein compression, and more elfective drilling can be achieved by exploiting this finding.

The present invention pertains particularly to a multicutter element rotary drill bit in which each cutter element comprises an assembly of cutters. The different cutter assemblies are distributed around and supportedby the lower portion of the body of a bit in substantially the same manner as presently conventional cutter elements are mounted and supported. The individual cutters :in each assembly, however, are further selected'and arranged so as to exploit the tensile Weakness of rock structures.

To effect the desired tensioning efiect, each cutter assembly of the present invention includes a pair of downwardly diverging cutters which are adapted to rotate and travel around the bottom of a borehole. Each pair of such cutters is arranged so that the cutting contact points of'the cutters are spacedfrom one another along a ;line extending radially and-laterally from the longitudinal centerline of the bit proper. i The cutters may be'sha rpedged disc cutters,but they are preferably provided with a toothed or corrugated rimto insure a rotational movement. Furthermore, suificient flexibility is provided within the cutter bearings or other portions of the general supporting structure to .enablethe cutters to splay or spreadlaterally from one another to a slight extent when points of the intermediate cutter and of the inclinedcntfters in each cutterassembly lie in substantially a common plane withthelongitudinal axis of the bit proper. Fur- .thermore, vthe lateral distance between the cutting con- .tact points ofthe inclined ,cutter elements in each cutter assembly should be such that the eifectof theinclined load application, applying .a horizontal loading to the ,formation, willextend at leasthalf the lateral distance. For conventional'loads and axis inclination angles, spacings of about 1,53 .5 inches are desirable. f

By obser'vingthe aboveeonditions, the centralfroller tween this cutter and the bottom of a borehole.

semblies. defines the outer wall surface of each socket or recess;

Patented Sept. 5, 1961 cutter in each cutter assembly acts to apply a vertical thrust to a section of a 'formationwhich is under very distinct tensile loading. In other Words, each central roller cutter acts upon a portion of a rock or other forma' tion which has been subjected to a highly tensile-stressed condition. The drilling effectiveness of the over-all bit is thereby greatly'enhanced.

As noted above, it is contemplated that the cutter as semblies of the present invention are spaced and arranged in the lower portion of a bit in much'the same manner as conventional multi-cutter rotary bits. In other words, the individual cutter assemblies are distributed around the lower surface of a bit body so'that a drilling action is effected against the entire bottom surface of a borehole during each rotation of the bit. f

The nature of the present invention may be better understood by reference to the attached drawing illustrating a preferred embodiment of the invention which is conte'mplated to'constitute the best mode of practicing the invention.

FIGURE 1 shows a bottom view of a multi-cutter element rotary bit employing the principles of this invention. FIGURE 2 is a partially sectioned view of the bit in FIGURE 1 taken along the section lines 22.

FIGURE 3 is a partially sectioned view taken along the section lines 33 of FIGURE 1. H

FIGURE;4 is an enlarged sectional view of one of the cutter assemblies shown in the preceding figures.

i FIGURE 5 is a view taken along the section lines 5-.- of FIGURE 1. 1

Referring-to the various figures, it may be seen that the main structural components illustrated include a bit body 10, roller cutter 13, frustoconical cutters 14 and 15, and disc cutters 16 and 17. Only one cutter assembly in eachfigure has been provided with legends for-its the drill string. Positioned around the lower surface of the body of the .bit are aplurality of recesses or sockets'22-each recess or socket being adapted to receive one of the cutter as- A lower outer-portion 23. of the bit body 10 and a lower central portion 24 of the body defines the :in-

nerwwall portion thereof. The outer lower portions 23 are sometimes referred to in the art as the shanks of.

a drill hit. As mentioned above, a separate branch drilling-fluid course 21 connects each recess or socket 22 with the central course 20.

The central supporting member 12 of each cutter assembly is in elfect a-wedge-like member with two laterally opposite, inclined side surfaces. Referring especially .tO. FIGURE .4, a shaft or pin 25 inclines upward and outward from the outer wall surface 28 of the member 12 to the adjacent shank portion 23 of the bit body. As 'in conventional bit design, at least one end of the shaft 25 'is welded orotherwise rigidly secured. J

Mounted on the shaft 25 is a disc cutter 16 which is freely rotatable thereon by virtue of the ball bearing 30. "The outer periphery of this cutter may-as mentioned 'earlierbe simply sharp-edged in character; but it is preferably provided with corrugations, notches, teeth or other suitable means for promoting a rolling contact be- While a pair'of the disc cutters just described is generally suflicient in each cutter assembly to realize the objects of this invention, it is preferred to use each such cutter in combination with a frusto-conical toothed cutter. Referring to FIGURE 4, for example, frusto-conical cutter '14 is mounted on shaft 25 between the disc cutter 16 and the wedge member 12. It is frnther preferred that these two cutters (i.e., cutters 14 and 16) be keyed together as by means of a peg 32. The frustoconical cutter not only enhances the drilling action of the cutter assembly by virtue of its cutting teeth, but it also promotes rotational movement of the disc cutter 16. Like disc cutter 16, frusto-conical cutter 14 is preferably supported on shaft 25 'by a ball bearing so as to enable this cutter to rotate freely upon the shaft. As just described in connection with the disc cutter 16 and the frustoconical cutter 14, another frusto-conical cutter 15 and a disc cutter 17 are mounted on a shaft 29 interconnecting the opposite side surface of the wedge element 12 to the lower center portion 24 of the bit body '10.

As shown in the various figures, the disc cutters on each side of the wedge elements in each cutter assembly are inclined toward one another so as to diverge downwardly. In other words, the longitudinal axes of these cutters (or the axes of shafts upon which they are mounted) incline upward and away from their wedge elements. The angle of inclination should be between about and 20, and preferably between 12 and 16.

be about /2 inch above the disc cutters. Thus, as the assembly of FIGURE 4 is placed against a rock surface,

the disc cutters contact the surface first and induce a tension in the surface. Loading on the assembly then causes the assembly to flex and eventually enables the frustoconical cutters and the roller cutter to approach and contact the rock. The two inner cutter assemblies of the bit may be substantially identical with the two outer assemblies, but they should be positioned inward therefrom so as to drill the center portion of a hole.

Further referring to the general arrangement of the cutters in each cutter assembly, the cutting contact points of all of the cutters in the assembly should lie in a common plane with the longitudinal axis of the bit. By observing this arrangement, ready rotational movement of the cutters is promoted; and element wear is minimized. Furthermore, maximum advantage is taken of the tensioning effect generated by the disc cutters 16 and 17. In some instances, it may be desirable to toe-in the two disc cutters in each cutter assembly, and toe-in angles of up to about 5 are contemplated. In any case, however, the cutter contact-point alignment described above I should be maintained. The term toed-in as used herein Positioned laterally between the oppositely disposed,

inclined cutters of each cutter assembly-and supported by the wedge-shaped member 12-is another cutter element 13. This cutter is preferably a geared or toothed roller-type cutter and is rotatably mounted by means of a ball bearing upon shaft 35. Shaft 35 is supported rigidly by member 12.

With respect to the general arrangement of the cutters in each cutter assembly, it is necessary that the cutting contact points of the two disc cutters 16 and 17 in each cutter assembly protrude or extend beyond the cutting contact point of the roller cutter 13 relative to the longitudinal axis of the bit proper. By observing this condition, the two disc cutters exert laterally opposite forces which induce a tensile stress within the rock structure lying between these two points. Suflicient flexing quality is also provided within the general supporting structure--e.g., within the shafts 25 and 29, the central supporting member '12, and the shank portions 23 and 24 (see FIGURE 4)--to enable the disc cutters 16 and 17 to splay or spread away from one another with the application of a conventional 'load. Thus, when loading and spreading of the disc cutters take place, roller cutter 13 brings into play a downward thrust which is exerted directly against a highly tensile-stressed rock structure. This combination of forces and stresses results in very rapid rock failure.

When frusto-conical cutters 14 and 15 are used in combination with disc cutters 16 and 17, it is preferred that the cutting contact points of these additional cutters also be recessed from the contact points of the disc cutters in order to preserve the tensioning effect of the disc cutters.

As illustrative of the relative positions of the various cutters in a cutter assembly of this invention, attention is directed to the case in which a bit of the type shown in the attached figures is adapted to drill a 9-inch diameter ihole. Referring specifically to one of the two outer curter assemblies, the outer disc cutter in the assembly should be positioned such that its cutting contact point is substantially 4.5 inches from the center line of the bit. The cutting contact point of the inner disc cutter may then be about three inches in from that of the outer disc the assembly-viz., cutters 14 and 15 in the assembly'of FIGURE 4qshould be about A inch above the disc cutters 16 and 17 when the assembly is in a 'relaxe'd ofnonstressed condition. Similarly, the roller cutter I3 should is intended to mean that the front portions of the cutters are closer together than the rear portions.

In operation, the bit described above'is attached to the lower end of a string of drill pipe by means of a threaded connection 9. The resulting assembly is then lowered within a borehole until the bit rests against the bottom of the hole. At this point, rotation of the bit is started, and drilling fluid is pumped down through the drill string and thence through the passageways 20 and 21 to the cutter assemblies. The bit is then loaded by releasing some of the weight of the drilling system from the rig or other supporting structure at the surface of the earth.

. As a load is applied to the bit, the disc cutters 16 and 17 in .the various cutter assemblies initially receive substantially the entire load. And, due to the inclined disposition of the disc cutters in each cutter assembly, op-

positely directed radial stresses are developed within the formation or rock underlying each assembly.

When the loading on the bit has increased to a predetermined value, the cutter shafts or other supporting structure have flexed sufiiciently to enable the disc cutters to spread slightly. This spreading of the disc cutters, in turn, enables the roller cutter 13and the frusto-conical cutters 14 and 15--in each cutter assembly to bear against the underlying rock structure. As described earlier, this interplay of thrusts makes for an increased rate of rock failure-and thereby promotes rapid drilling.

It willbe understood that the foregoing description is concerned with a preferred embodiment of the invention, but this embodiment is subject to a variety of modifications, additions, subtractions, etc., without departing from the spirit or scope of this invention. Thus, while the above embodiment has been concerned with cutter assemblies in which a disc cutter such as cutter 16 is a separate entity from the adjacent frusto-conical cutter 14, it will be recognized that these two cutters may be fabricated as a single integral unit. It will further be recognized that many conventional forms of tooth design may be used in fabricating the teeth which are used on all of the cutters.

It is also to be noted that the wedge elements 12 of the various figures may be an integral part of the bit body,

'or they may be separate elements. FIGURE 5 shows how the bit body may appear when the wedge elements are made an integral part thereof as by welding the lower edges of the wedge elements to the bit body. In this figure, the cutter elements have been omitted to emphasize the construction of the body portion.

"Insofar as the asembly and construction of a bit of this invention are concerned, it is contemplated that a variety of conventional techniques may be employed.

For example, in the instance where the wedge elements are separate entities" from the body 'of a bit, the different cutter elements may be fabricated as sub-assemblies and the sub-assemblies thereafter welded in place in the bit body. To illustrate, and turning 'to FIGURES 1-4, the recesses Q2 may be formed directly in'the bit body; and the body may then be bored to form the necessary bearing surfaces for pins 25 and 29. Each separate wedge element may be drilled in a similar manner to form the other bearing supports for pins 25 and 29, and recesses for the cutters 13 may be provided as by milling. Each element 12 may be bored for a pin 35, and the pins 35 and cutters 13 may thereafter be inserted. Pins 35 may be welded in place; and cutters 14, 15, 16 and 17 may be placed on a suitable jig. These cutters and the wedge elements may then be assembled as sub-assemblies and the pins 25 and 29 inserted and welded over at their shaft ends. Each sub-assembly may thereafter be welded to the body of the bit.

The invention claimed is:

1. An improved drill bit comprising a body member attachable at its upper end to a string of well pipe, a plurality of recesses within the lower surface of said body member, a cutter element assembly within each recess, said recesses distributed around said lower surface to provide a working relationship between said cutter element assemblies, each cutter assembly comprising a central Wedge portion having laterally opposite, upwardfacing, inclined side surfaces, a separate shaft for each side surface of each wedge, each said shaft being mounted at one end in a side surface and at the other end in said body member, said wedge and said shafts being arranged within said recesses such that the axes of the shafts when extended intersect the longitudinal axis of the bit, the axis of the laterally inner shaft inclining upward toward the center of the bit, and the axis of the outer shaft pending downward toward the center of the bit, a frusto-conical cutter and a disc-type cutter on each shaft, each frustoconical cutter being positioned between its respective disc-type cutter and said wedge element, a recess within the lower portion of each wedge element, a laterally disposed shaft within each wedge recess with its axis substantially perpendicular to the axis of the bit, a roller cutter on said laterally disposed shaft, the lowest point of the periphery of each roller cutter and each frusto-conical cutter being recessed relative to the lowest point of the periphery of each disc cutter associated with its respective cutter assembly.

2. An improved rotary drill bit comprising a body 'mem'ber adapted at its upper end to be attached to a string of well pipe, a plurality of cutter assembly sockets in the lower end of said body member, each cutter assembly socket having lateral inner and outer wall surfaces, a cutter assembly supported within each socket and adapted for rotation around the axis of the bit, said sockets arranged around said lower end of said body member to provide a working relationship between said cutter assemblies, each cutter assembly comprising a supporting member, a shaft upwardly inclined relative to said body member supported at one end within said supporting member and at its opposite end within the lateral inner wall surface of ,the socket, the axis of the shaft intersecting the axis of the bit when extended, a second shaft supported at one end within said supporting member and with its other end within the lateral outer wall surface of each socket, the axis of said second shaft when extended intersecting the axis of the bit and extending and inclined upwardly therefrom, a disc cutter on each shaft, a truncated cone cutter on each shaft positioned between said disc cutter and said supporting member with the truncated portion of each cutter facing toward said supporting member, a cylindrical toothed cutter interposed between the truncated cone cutters in each said assembly and rotatably supported by said supporting member with its axis laterally disposed and intersecting the axis of the bit when extended, the cutting lation around the lower. end ofsaid body member, each cutter assembly comprising a central supporting member having two laterally opposite sides, at least one cutter element on each side of the supporting member, a central shaft for each cutter element supported at one end within the supporting member, said shafts converging downwardly toward said supporting member and lying in substantially the same plane, the outer end of each shaft supported within said body member, a laterally disposed cutter shaft supported at each end by said supporting member between the cutter elements on each side of the supporting member, a cylindrical cutter element mounted on said laterally disposed shaft with its cutting contact point recessed slightly from the cutting contact points of the side cutters, each cutter assembly being supported within said body member by means of said inclined shafts such that the axis of the bit and the axes of the cutters lie in substantially the same plane.

4. An improved cutter element for a multi-cutter element rotary bit including a bit body member which comprises a central supporting member having two laterally opposite sides, a separate inclined shaft connecting each lateral side of the supporting member to the said body member, said shafts converging downwardly upon said supporting member, a disc cutter mounted on each shaft, a laterally disposed shaft supported at each end by said supporting member between said disc cutters, a cylindrical cutter rotatably mounted on said laterally disposed shaft, the cutting contact point of the periphery of the cylindrical cutter recessed slightly 7 from the cutting contact points of the disc cutters adjacent thereto, said cutter element being mounted within said body member so as to rotate around the axis of the bit.

5. An improved cutter assembly for use in a multicutter assembly drill bit which comprises a central supporting member, two downwardly converging shafts attached at one end to opposite sides of said supporting member, a disc-type cutter otatably mounted on each shaft, a cylindrical cutter rotatably supported by said supporting member laterally between said disc cutters, the cutting contact point of the periphery of the cylindrical cutter being recessed relative to the cutting contact points of the disc-type cutters, the opposite ends of said shafts being adapted to be supported by said bit such that the cutting contact points of the cylindrical and disctype cutters in each assembly lie in a common plane with a longitudinal axis of the bit.

6. An improved multi-cutter element rotary bit which comprises a body member having a plurality of sockets disposed in the lower surface thereof, each socket adapted to receive a separate cutter element and arranged in said lower surface to provide a working relationship between the cutter'elements, each cutter element comprising a support member, two cutter shafts attached at one end to opposite sides of said support member and extending upward therefrom to supporting engagement with the surrounding socket, a disc-type cutter rotatably mounted on each shaft, a cylindrical cutter rotatably supported by said support member between said disc cutters and in a recessed position relative to said disc cutters, all of the cutters in each cutter element arranged such that the cutting contact points of the cutters fall in substantially a common plane with the longitudinal axis of the bit.

7. An apparatus as defined in claim 6 in which the support member in each cutter element is welded to the body member to be an integral part thereof.

8. An apparatus as defined in claim 6 in which each of 7 said cutter shafts extends upward at an angle between 5 and 20.

9. An apparatus as defined in claim 6 in which a frusto-conical cutter is rotatably mounted on each said cutter shaft between said support member and the disctype cutter thereon, said frusto-conical cutter being in a recessed position intermediate said cylindrical cutter and said disc-type cutter.

References Cited in the file of this patent UNITED STATES PATENTS 1 Sperry Jan.4, 1935 

